Show just disconnected device on previously connected

- This CL before, previously connected devices will show most
  recently connected devices and the maximum is 3.
  In this time, if next most recently connected device is disconnected.
  It's will not show on "previously connected devices", user needs go to
  "see all" page to found that device.
  This CL add rule to compare the priority of most recently connected
  device. If priority of next disconnected device is higher than
  currnect devices that on "previously connected devices".
  Let next disconnected device show on "previously connected devices".
- Update test case.

Bug: 157653997
Test: make -j42 RunSettingsRoboTests
Change-Id: I684501a20a67755b2196ba9d4b5565add01a5d01
Merged-In: I684501a20a67755b2196ba9d4b5565add01a5d01